Stackers are typically employed for the purpose of stacking signatures delivered thereto in the form of a signature stream of signatures arranged in "shingle" or imbricated fashion. The stacker is provided with a plurality of buckets which are guided about a closed loop path, typically by means of cam follower rollers arranged on the buckets which rollingly engage a closed loop cam recess. The buckets are maintained at spaced intervals about the closed loop path by means of drive chains, each bucket being linked to the drive chains by coupling links having one end pivotally connected to the bucket assembly and the opposite end pivotally connected to a substantially T-shaped link forming an integral part of the drive chains. The drive chains are typically moved by suitable motor means to advance the buckets through each of the regions of the closed loop path which typically comprise: a home position at which a bucket is located above the signature stream preparatory to intercepting the signature stream; an intercept position to which the bucket in the home position is abruptly moved to intercept the signature stream and divert the flow of signatures from the downstream bucket to the bucket now in the intercept position; a stacking region through which the bucket is moved downstream relative to the intercept position as it collects signatures; a drop region through which the bucket moves as it leaves the stacking region wherein the bucket is rapidly accelerated to drop out from beneath the signature batch accumulated thereon to enable the signature batch to fall upon an outfeed surface; and a return region through which the bucket passes in moving from the drop region to the home position in readiness for intercepting the next bundle.
The aforementioned connecting links which couple each bucket to the drive chain are each provided to compensate for any differences in the pitch centerlines of the closed loop cam recess and the closed loop drive chain.
The bucket imparts a force upon the chain which is applied to the pivot point of the T-shaped link forming part of the drive chain. Since this pivot point is offset from the pitch centerline, when a load is applied, a turning moment is created resulting in excessive play and less efficient power transmission.